feat: add structured error logging for webhook retry exhaustion

[dubemoyibe-star]

PR: Webhook Retry Exhaustion Error Logging

Summary

Updated the webhook delivery retry-exhaustion log path to emit a single, structured error-level log entry with full operator context. The log is emitted exactly once when a webhook exhausts all retry attempts and is flagged as failing. Individual retry failures continue to use the existing warn-level log.

Motivation

When a webhook exhausts all delivery retries and is flagged as failing, operators need enough structured context to identify the webhook and manually investigate the callback URL. The previous log entry was missing event_type and used attempt_number instead of total_attempts, and did not include a flagged_at timestamp. This made it harder to correlate with other system events and to determine when the webhook was suspended.

Changes

Modified Files

• src/modules/webhooks/webhook.service.ts
• src/modules/webhooks/webhook.service.test.ts

Behavior Changes

Before	After
Log field attempt_number	Log field total_attempts
No event_type in log	event_type included
No flagged_at in log	flagged_at included (ISO 8601 timestamp)
No validation that log emits exactly once	Test asserts logger.error called exactly once
Callback URL absent from exhaustion log	Callback URL remains absent (never added)

Structured Error Log Fields (on exhaustion)

Field	Type	Description
webhook_id	string	The webhook registration ID.
creator_id	string	The creator whose webhook failed.
event_type	string	The event type being delivered ("BUY" or "SELL").
total_attempts	number	Total number of delivery attempts made.
last_error_code	string	The last error message from the failed delivery.
flagged_at	string	ISO 8601 timestamp when the webhook was flagged as failing.

Callback URL Privacy

The callback URL never appears in the exhaustion log. The existing retry warn log continues to use maskWebhookUrl() to log only the origin (e.g., https://hooks.example.com).

Implementation Details

The change is confined to the attemptDelivery() function in webhook.service.ts. When retries are exhausted (attempt >= maxAttempts):

1. The webhook record is updated (isFailing = true).
2. All pending WebhookEvent records are marked as FAILED.
3. A single logger.error() call emits the structured log with the fields listed above.
4. The log is emitted exactly once per exhaustion event, after all retries have failed.

Individual retry failures continue to emit logger.warn() with backoff details and a masked callback URL.

Formatting

Ran pnpm run format to format the codebase in prettier style

Testing

Updated webhook.service.test.ts to assert:

• logger.error is called exactly once.
• The log object contains webhook_id, creator_id, event_type, total_attempts, last_error_code, and flagged_at.
• total_attempts equals WEBHOOK_RETRY_MAX_ATTEMPTS.
• flagged_at is a valid string (checked via expect.any(String)).
• Callback URL is not present in the exhaustion log fields.

Verification

Run the targeted test:

pnpm test -- src/modules/webhooks/webhook.service.test.ts

Closes #587